Health challenges don't end when Ebola patients recover from the virus. A study is exploring why that is.

When Dr. Ian Crozier was released from Emory University Hospital in October, weeks after he was infected by the Ebola virus in Sierra Leone, there was no sign of the deadly pathogen in his blood.

But in December, the American physician returned to Emory with inflammation and elevated blood pressure in one eye. Fluid drained from the eye contained the Ebola virus.

Similar eye health problems have been reported in West Africa among the more than 16,000 survivors of the largest Ebola outbreak in history, but doctors don't know why. Researchers at the Johns Hopkins Wilmer Eye Institute are among those who plan to find out.

A research partnership between U.S. and Liberian health officials has launched a study to learn more about the long-term health consequences of Ebola, including the risks of passing the virus to close contacts and sexual partners, and the development of long-term immunity to the virus. Wilmer researchers are to lead efforts to explore the virus' effects on eye health.

The unprecedented spread of Ebola throughout West Africa last year has created the best opportunity yet to understand the virus' lingering effects in survivors. Past outbreaks were significantly smaller and more isolated, and left far fewer survivors.

The outbreak also provides an opportunity to fill gaps in vision care, researchers say, much as the initial spread of the disease revealed failings in the larger health care system.

"The effects of the Ebola virus have been tragic," said Dr. Allen Eghrari, an assistant professor of ophthalmology at the Wilmer institute. "We hope this can be an opportunity to really build as we move forward."

The immediate toll of the Ebola outbreak was the more than 11,000 lives it took in Liberia, Guinea and Sierra Leone. But for many of those who contracted the disease and survived, health problems linger, according to the World Health Organization, which has reported cases of clouded or lost vision, headaches, fatigue and joint, muscle and chest pain.

Texas nurse Nina Pham contracted Ebola from a Liberian man who carried the virus to Dallas and was treated at the National Institutes of Health Clinical Center in Bethesda. She told the Dallas Morning News that she has suffered hair loss, body aches and insomnia since her release in October.

Doctors have seen "post-Ebola syndrome" in previous outbreaks, but understanding of the condition, which can cause long-term disabilities, is limited. Before last year's outbreak, the largest Ebola epidemics infected several hundred people, and in some cases had mortality rates of more than 80 percent.

The dramatic scope of the recent outbreak meant both more opportunity to study Ebola's health effects, and a greater need to understand them, said Dr. Christopher Brady, another assistant professor of ophthalmology at the Wilmer institute.

For survivors in West Africa, he said, such health problems can be serious impediments to livelihood.

"People who were surviving tended to be the younger people," Brady said. "If they were going to have vision loss, it was really going to impact their productivity for the rest of their lives."

The National Institute of Allergy and Infectious Diseases and the Liberian Ministry of Health launched a study of the survivors last month. They planned to enroll about 7,500 people — 1,500 Ebola survivors of all ages and 6,000 of their close contacts.

Researchers plan to check in with the participants every six months for up to five years to closely monitor Ebola antibodies, whether the survivors can transmit the virus, and if so, whether those contacts get sick with Ebola.

Brady and Eghrari are helping to lead a segment devoted to eye health. The study will include comprehensive exams to learn more about how and why the virus affects vision.

"We don't even know what the problem is," Brady said. "The major issue is to sort out exactly what are the various effects of Ebola on the eye."

Theories of the effects, according to the World Health Organization, include damage to the cornea or to ocular nerves.

"There's a significant need to characterize what parts of the eye [are affected] and what is the range of complications that can occur," Eghrari said.

The study is based in Liberia, and the researchers hope it will also address overall eye care there. The effort will require training Liberian health care workers on how to conduct eye exams, and also making ophthalmology equipment more widely available.

"It's a valuable opportunity for us to work together with Liberian eye care providers to not only study what is needed, but to build capacity in Liberia as well," Eghrari said. "The eye needs are significant both from the immediate effects of the Ebola virus as well as other needs."